The present invention relates to liquid crystal displays and, more particularly, to a novel multi-color liquid crystal display and to a display system using said display.
It is known to the art to provide a liquid crystal display capable of providing a plurality of different viewable colors. Prior art displays of this type generally suffer from low optical efficiency if a given area must be devoted to a particular color component. If interference effects are used, the display will generally have a relatively poor angle-of-view. Similarly, if transverse-type dichroic dyes are guests in the liquid crystal host of the display, a relatively low color purity will result. Further, color choice is relatively limited with almost all prior art displays combining several guest dichroic dyes.
One technique, previously utilized for obtaining a plurality of colors in a given area of a liquid crystal display, is the use of a mixture of so-called longitudinal and transverse dyes having different spectral absorption characteristics. In one orientation of the host liquid crystal material, the absorption of one dye predominates, while in another liquid crystal host orientation, the absorption of the other dichroic dye predominates. Thus, only two colors, of relatively low saturation, are possible.
In another prior art approach to a multi-color matrix display, a matrix of cells is provided with different elements in each cell controlling different primary colors. For example, each cell may contain a triad of elements with each element of the triad having a different one of red, green and blue filters and with a black guest dichroic dye being utilized to control light transmission through any one of the different-colored elements of the cell triad. Because only one of the three elements can contribute to a given color of cell light output, this form of display has a limited efficiency.
It is therefore highly desirable to enable each area, or cell, of the display to produce one of a wide variety of colors, with high purity and by a purely electronic control which can be implemented in a display system completely by circuitry, external to the display itself, driving each of the display cells.